<template>
    <ul class="list">
        <li class="item" v-for="item of letters" :key="item" @click="handleLetterClick" :ref="item"
         @touchstart.prevent="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd">{{item}}</li>
    </ul>
</template>

<script>
export default{
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    computed:{
        letters(){
            const letters=[]
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    data(){
        return{
            touchStatus:false,
            startY:0,
            timer:null
        }
    },
    updated(){
        this.startY=this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick(e){
            this.$emit("change",e.target.innerText)
        },
        handleTouchStart(){
            this.touchStatus=true
        },
        handleTouchMove(e){
            if(this.touchStatus){
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer=setTimout(()=>{
                    const touchY=e.touches[0].clientY-79
                    const index=Math.floor((touchY-this.startY)/20)
                    if(index>=0 && index<this.letters.length){
                        this.$emit('change',this.letters[index])
                    }
                },16)
                
            }
        },
        handleTouchEnd(){
            this.touchStatus=false
        }
    }

}


</script>

<style lang='stylus' scoped>
    @import '~styles/varibles.styl'
    .list
        position:absolute
        display:flex
        flex-direction:column
        justify-content:center
        right:0
        top:1.58rem
        bottom:0
        width:.4rem
        .item
            line-height:.4rem
            text-align:center
            color:$bgColor

    


</style>